With the aim of understanding the mechanisms of DNA evolution the following interrelated research projects are proposed: I. Theoretical studies. Mathematical models will be developed for estimating the number of nucleotide substitutions and the numbers of synonymous and nonsynonymous substitutions between two homologous sequences. II. Statistical analyses of sequence data. (1) Patterns of nucleotide substitution will be studied in various regions of DNA, including regions with no apparent function, regions for protein coding genes and regions for RNA genes. The results will be used as empirical bases for developing models for estimating the number of nucleotide substitutions between sequences, for predicting the base contents in various regions of DNA and for evaluating models for the molecular basis of point mutations. (2) Evolution of pseudogenes. The aims are to obtain the neutrality standard for the rate of nucleotide substitution, to estimate the date of the duplication event leading to the pseudogene and the functional gene and the date the pseudogene became nonfunctional, and to tabulate the relative frequencies of different molecular lesions that can prevent a gene from expression. (3) Rates of nucleotide substitution will be estimated for nuclear DNA, mitochondrial DNA, and chloroplast DNA. The results will be compared to see if there are significant differences in substitution rates among the three kinds of genomes and if yes, to infer the main cause for the differences. (4) Statistical analyses will be done to characterize deletions and insertions in sequence evolution with respect to their frequecy and location of occurrence, the size of gap events and the relative frequencies of spontaneous deletions and insertions.